The present invention relates generally to testing semiconductor integrated circuit packages, such as printed circuit boards, substrates, and the like during various stages of manufacturing. More particularly, it relates to a test apparatus for probing the ends of pins having multiple diameters and different pin tip configurations.
In the microelectronic industry, integrated circuits require testing prior to being packaged to determine not only that they are fully functional but that they also conform to specifications to which they are designed. Testing is an expensive part of the fabrication process. The operability of every circuit within the integrated circuit package and of every I/O must be tested since even a single failure to conform to the design specification renders the entire integrated circuit or package unusable for its intended application.
In the semiconductor industry, chips are mounted on vehicles called substrates. They, typically, plug, into a larger printed circuit board by way of an array of pins mounted on the substrate and which number anywhere from a few to several thousand pins. When testing involves a circuit board, a card, or a substrate upon which the chips are mounted, a wire type probe tip is held against its surface until contact is made. A measurement is then taken, the result of which is used to test or characterize the device or package. These wires are an integral component of a probe which, in turn, forms part of an automated or manually operated probing machine. These machines are provided with an actuator or servo mechanism that moves an arm in the x, y and z directions, and which holds an apparatus for capturing the probing pins that make the necessary electrical measurements and check for electrical integrity. They, further, ascertain whether the device or package under test meets certain criteria in terms of functionality, quality control and performance standards.
Several types of probes are commercially available, such as, e.g., cantilever, micro-structure type, or the previously mentioned (wire type) probe tips. The tip of the latter consists of a piece of very thin wire mounted to some type holding device or fixture. This type of probing apparatus is ideal for probing flat surfaces, such as C4(controlled collapse chip connector) solder balls, electrical pads of substrates, printed circuit boards, and the like. An example of a typical sign is described in U.S. Pat. No. 5,929,521 which will be discussed in detail hereinafter.
Probes in the form of a wire generally end in a cylindrical or cone shaped termination, allowing contact with the C4 solder bumps or the surface of the device or package typical of surface mount technology, or any other type of substrate under test. By way of example, an apparatus may be required to test an electrical printed circuit board (referred to as daughter card) that plugs onto another larger printed circuit board by way of an array of pins mounted on the underside of the daughter card, and which plugs into a socket on the larger board. During manufacturing of the daughter card, electrical measurements are taken to verify the electrical integrity of the card to ensure that the final product meets the electrical specifications and the integrity of the pins making the connections necessary between the two boards. Accordingly, there is a need for a device (or vehicle) that has pins attached to it, or mounted for the purpose of providing the necessary electrical connections.
While there exists several apparatus and methods for probing a surface, the success achieved by each apparatus in making contact with the end of a pin is not always adequate. A problem exists with establishing contact with pins that are not always perfectly vertical or not perfectly centered. Thus, the end of the pin is oftentimes not positioned on the device exactly where it should, making contact with the center of the pin difficult. Accordingly, conventional setups do not always yield the desired measurement since contact is not achieved altogether or, at best, it is only partially made.
An added problem exists when pins are placed on a device having a positional tolerance. This tolerance permits a certain amount of movement of the pin end away from its theoretical ideal location on the device. Moreover, the geometry of the pin termination also varies from design to design. Some pin ends are rounded, some have a chamfer to ease the insertion of the pin into the socket in which it is to be plugged into during final assembly. This radius or chamfer on the end of the pin oftentimes causes the probe tips to slip or glide off, causing erroneous readings. The narrowing of the termination of the pin reduces the flat surface area available at the end of the pin. Thus, the probe makes no contact with the flat surface that is perpendicular to the center line of the probe tip wire. Accordingly, typical probe tips are not suited to contact a curved surface, unless the pin end resides at its theoretical ideal location to provide a tangent plane perpendicular to the center line of the probe tip. Furthermore, a coaxial condition must exist between the pin under test and the probe tip wire. Probe pins of this nature are easily bent or they become misaligned during manufacturing because the slightest contact with the pin causes the end of the pin or probe wire tip to move away from its nominal position. This bending is enhanced even further by the very small diameter or size of the probe pin wire or tip.
Referring back to the aforementioned U.S. Pat. No. 5,929,521, the probe described suffers from similar limitations which are characteristic of many conventional probe designs. In the probe apparatus described therein, the pins fail to take into account the geometric tolerance that enables moving the pin about while still remaining within specifications. It requires a multi-step etching process which is difficult to control and fabricate. Further, the design of the probe requires layers of conductive material, and the probe fails to contact the full array of C4s since it lacks the ability of accounting for grid tolerance, (in view of the grid tolerance created by the etching process). Finally, it is not cost effective.
In view of the foregoing limitations found in the art, it is an object of the invention to provide an apparatus for reliably probing ends of pins having multiple diameters and different pin tip configurations.
It is another object to provide an apparatus for probing flat surfaces such as C4 solder balls arranged in an array grid formation and attached to the chip, electrical pads of substrates, printed circuit boards, or to any other device provided with electrical contact points that are reasonably flat.
It is still another object to provide a probe tip suited to contact curved surfaces.
It is a further object to use a simple machining technique to simplify the manufacturing requirements for the probing machine, increase the ease of its use and lower its cost.
It is yet another object to provide a probe machine easily adapted to any pin configuration, to any chip and packaging design without having to redesign the probe with each new design.
The above discussed drawbacks, and deficiencies of the prior art are overcome or alleviated by utilizing the pin probe of the present invention, wherein the probe apparatus creates a self-centering contact, such that its shape captures the pin throughout its tolerance range and treats it as if it were ideally installed. Thus, the probe of the present invention has an extra degree of freedom that provides ease of movement and which can be tailored to fit any particular use and application.
The design of the probe of the present invention is straight forward. It is provided with a rigid mount that can be attached to any auto or manual servo or actuator. The probe is designed to have a built-in tolerance that allows locating pins and balls in a grid within their respective tolerances and still make good contact.
In another aspect of the invention, there is provided a conical, parabolic or hyperbolic recess giving it a rounded end and tapered sides that allows pins and C4s to move within their grid tolerance and still be contacted, allowing accurate measurements to be taken.
One variant of the probe is an apparatus that is round and mounted to a chucking device and put into contact with the device to be tested or examined.
In yet another aspect of the invention, there is provided a probe assembly that includes: means for providing multi-direction motion; and means for making electrical contact to pins of a device or package under test and for probing the pins, these means including a shaft terminating in an end section provided with a conical shaped recessed area.
In still another aspect of the invention, there is provided a gang probe assembly that includes: a servo mechanism providing multi-direction motion; and a plurality of pin probes arranged in an array formation attached to the servo mechanism and making simultaneous contact with an array of pins attached to a device or package under test, wherein each of the pin probes includes a shaft having an end section provided with a recessed conical section.
These and other objects, aspects and advantages of the invention will be better understood from the following detailed description of a preferred embodiment to be described hereinafter when taken in conjunction with the appended drawings, in which:
FIG. 1 is a perspective view illustrating the preferred embodiment of the probe to a device provided with pins, in accordance with the present invention.
FIG. 2 is a side view schematic showing a cut away view of the probe pin in contact with the device pin. Also shown is the probe mounting block and the servos, illustrating the relative position of the probes when in contact with the device.
FIG. 3 is an exploded view of the probe. It also shows a probe mounting block and retaining screw for mounting the probe to the manufacturing or testing device.
FIG. 4 is an exploded view of a second embodiment of a probe according to the invention, showing the mounting block and retaining screw for mounting the probe to the manufacturing or testing device.
FIG. 5 shows a gang probe utilizing the pin probe to contact multiple pins of a device such as a daughter board, substrate, and the like.
FIG. 6 is a schematic diagram of a pin probe used for collision avoidance and which is provided with a pin probe having an oval shaped bottom and a conical recessed area.